TRPA1 analgesia is mediated by kappa opioid receptors
TRPA1 expressed in peripheral sensory neurons is important for nociception. Pharmacological inhibition or genetic ablation of TRPA1 profoundly reduces normal behavioural sensitivity to noxious cold and mechanical stimulation, as well as sensory neuron responses to mechanical stimulation. TRPA1 inhibition also reverses cold and mechanical hypersensitivities in chronic pain models in vivo. Here we demonstrate that these striking effects of TRPA1 inactivation result from an increased constitutive activity of kappa opioid receptors (KOR) co-expressed with TRPA1 in sensory neurons. Inhibition of KOR in Trpa1-/- mice restores nociception and neuronal activity to the levels observed in wild-type mice and reverses the analgesic effects of TRPA1 antagonism in naive mice and in neuropathic and inflammatory pain conditions. TRPA1 regulation of KOR activity in sensory neurons provides a novel mechanism to produce peripherally mediated analgesia. Our findings suggest that TRP channel regulation of constitutive GPCR activity, may be a process of general physiological importance.